When the Voyager 1 and 2 spacecraft flew by Saturn in 1980 and 1981, they were able to pay only fleeting attention to Titan, the second largest moon in the solar system (larger even than the planet Mercury) and the only solar system moon with an appreciable atmosphere. These images are from subsequent Titan flybys in 2005 and 2006. - Image credit: NASA / JPL / University of Arizona
Pluto's giant moon Charon may have had a buried ocean. In July of 2015, NASA's New Horizons spacecraft will be the first to visit Pluto and Charon, and will provide the most detailed observations to date.
This global view of Jupiter's moon, Io, was obtained during the tenth orbit of Jupiter by NASA's Galileo spacecraft on 19 September 1997 at a range of more than 500,000 km (310,000 miles). Io (which is slightly larger than Earth's moon) is the most volcanically active body in the solar system. Colors are enhanced. Credit: NASA/JPL/University of Arizona